Stereochemical Control via Chirality Pairing: Stereodivergent Syntheses of Enantioenriched Homoallylic Alcohols

Unusual Enantiodivergence in Chiral Brønsted Acid‐Catalyzed Asymmetric Allylation with β‐Alkenyl Allylic Boronates

We report herein a rare example of enantiodivergent aldehyde addition with β-alkenyl allylic boronates via chiral Brønsted acid catalysis. 2,6-Di-9-anthracenyl-substituted chiral phosphoric acid-catalyzed asymmetric allylation using β-vinyl substituted allylic boronate gave alcohols with R absolute configuration. The sense of asymmetric induction of the catalyst in these reactions is opposite to those in prior reports. Moreover, in the presence of the same acid catalyst, the reactions with β-2-propenyl substituted allylic boronate generated homoallylic alcohol products with S absolute configuration. Unusual substrate-catalyst C-H⋅⋅⋅π interactions in the favoured reaction transition state were identified as the origins of observed enantiodivergence through DFT computational studies.

Chiral Phosphoric Acid Catalyzed Conversion of Epoxides into Thiiranes: Mechanism, Stereochemical Model, and New Catalyst Design

Computations and experiments leading to new chiral phosphoric acids (CPAs) for epoxide thionations are reported. Density functional theory calculations reveal the mechanism and origin of the enantioselectivity of such CPA‐catalyzed epoxide thionations. The calculated mechanistic information was used to design new efficient CPAs that were tested experimentally and found to be highly effective. Bulky ortho‐substituents on the 3,3′‐aryl groups of the CPA are important to restrict the position of the epoxide in the key transition states for the enantioselectivity‐determining step. Larger para‐substituents significantly improve the enantioselectivity of the reaction.